reptile7's JavaScript blog is Andrew Peak's personal technical writing project: it focuses on JavaScript and the analysis of JavaScript scripts, although HTML, CSS, and anything else related to coding for the Web are also fair game.

How 'bout them target attribute values, huh? new window? resource window? Seem suspicious, don't they? To be sure, they're not standard, but - at least with respect to HTML - they're not invalid, either.

• CDATA is defined in Section 6.2 ("SGML basic types") of the HTML 4.01 Specification. A CDATA string can contain any Unicode characters, including white space characters, and also character references (e.g., &pound; for £); however, before you add a target="@#$%" attribute to your Web page, I draw your attention to Section 6.16 ("Frame target names") at the bottom of the page, which states, [F]rame target names (%FrameTarget; in the DTD) must begin with an alphabetic character (a-zA-Z). User agents should ignore all other target names. (So as to why the target attribute has a CDATA data type and not a NAME data type, well, you'll have to ask Dave Raggett about that.)

according to which a NMTOKEN string must begin with an alphabetic character, an underscore, or a colon, followed by zero or more NameChar characters (letters, digits, periods, hyphens, etc.). NameChar characters do not include white space characters, and thus the new window and resource windowtarget values are actually invalid from an X(HT)ML standpoint.

4. If any target attribute refers to an unknown frame F, the user agent should create a new window and frame, assign the name F to the frame, and load the resource designated by the element in the new frame.

It follows that there's nothing special about the new window and resource windowtarget values - we could set a link's target attribute to Bond_007 (but not 007_Bond) and the link will open in a new window as long as there isn't another window named Bond_007 open on the screen.
FYI: If an empty string is assigned to the target attribute (target=""), then the link's href file will not be loaded into a new window but into the current window.

Interestingly, Mozilla pooh-poohs the use of target="_blank", arguing that
(a) it's inefficient, more specifically, a given target value should be reusable by other links in the document, which is not the case for the _blank value, and
(b) it's semantically unsatisfying: target="demoWindow" would be a better choice for a demo page link, for example.
(For that matter, Mozilla argues against loading files into new windows more generally.)
But I'm sure Mozilla would agree that there's nothing terribly wrong with target="_blank" if you only use it once or twice in your document.